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Title: The pyrolyses of alkyl nitrites
Author: Milne, Raymond T.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1973
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The apparent disagreement between previous kinetic and thermochemical data for D (RO-NO) can be resolved in terms of the effect of two parallel reactions: a homo-geneous radical split and either a homogeneous or a heterogeneous molecular elimination process. The object of this study was to isolate and follow the rate of breaking of the RO-NO bond. For R = t-Bu, i-Pr or Et, this is achieved by using low nitrite con- centrations (10-5 10-4 M) and low extents of decomposition in the presence of a high total pressure of CF4 (∼ 0.9 atm) in order to maintain all unimolecular decomposition and bimolecular recombination processes as near to their limiting high pressure rates as possible. Under these conditions the first order, homogeneous rates of acetone, acetaldehyde or formaldehyde formation are a direct measure of (1). (2 ) RONO ==== RO + NO (1 ) RO ? decomposition products (3) For R = Me, isobutane is used as a radical trap (4) and the methanol formed gives a direct MeO + tBuH ? MeOH + t-Bu (4) measure of (1). In all four cases, addition of large amounts of NO in place of isobutane or CF4 almost com-pletely suppresses the radical split, thus demonstrating the high efficiency of NO as a radical trap under these conditions. Process (3) occurs in the absence of (2) when the nitric oxide concentration is low. The heats of formation of t-butyl and isopropyl nitrites were determined by bomb calorimetry and ?H1,2 calculated using established values for ?H f(RO). The kinetic and thermochemical values for ?H1,2 are now in complete harmony. It is concluded that E2 = o 1 Kcal/mole and that D(RO-NO) = (41.5 1) Kcal/ mole. From ?S1,2, values for k2 are calculated to be ∼ 1010.3 M-1 s-1 and process (2) is established as a useful reference reaction. When R = tBu, the parallel reaction is the six- centre elimination of HONO. Process (5) is tBuONO isobutene + HONO (5) shown to be a homogeneous first order reaction and there is good agreement between the observed and calculated A-factors. When R = i-Pr , Et or Me, the elimination of HONO, when possible, is prohibited thermochemically; however, the heterogeneous first order elimination of HNO occurs, accompanied by either acetone, acetaldehyde or formaldehydes The occurrence R1R2CHONO R1R2CO + HNO (6) of the elimination process reduces the value of the alkyl nitrites as thermal sources of RO; of the four cases studied, methyl nitrite alone may be described as a good source of RO under certain conditions. Process (6) is not possible in the case of t-butyl nitrite. The CH3 - NO bond dissociation energy is determined via equilibrium (7, 8) and the experimental heat of combustion of trans dimeric nitrosomethane. D (CH3 - NO) is (8) (CH3NO)2 == 2CH3NO (7) discussed in relation to the NO inhibition of the gas phase pyrolyses of organic compounds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available